Ethernet Tree (E-Tree) service is defined in Metro Ethernet Forum (Metro Ethernet Forum, MEF) as an Ethernet virtual connection (Ethernet Virtual Connection, EVC) service. It has the following features:
One root (Root) node corresponds to multiple leaf (Leaf) nodes, and multiple root nodes may exist.
The Ethernet fames from a root node may be received by another root node or any leaf node, and the Ethernet frames from a leaf node may be received by any root node.
A leaf node cannot communicate with another leaf node and they need to be isolated.
The asymmetric virtual local area network (virtual local area network, VLAN) technology may implement E-Tree services in Ethernet. In the asymmetric VLAN technology, a root node and a leaf node access a switch in untagged mode by using a root port and a leaf port respectively; in the switch, a PVID and a member set (member set and untagged set) is configured for each access port, and an egress port set for forwarding is configured respectively. When Ethernet frames enter the switch from the port accessed by the leaf node, the Ethernet frames are tagged with the port VLAN identifier (Port VLAN ID, PVID) corresponding to a leaf VLAN, then forwarded to the port accessed by the root node, and finally transmitted to the root node. When the Ethernet frames enter the switch from the port accessed by the root node, the Ethernet frames are tagged with the PVID of the corresponding root VLAN, and then sent to all members in the member set, that is, all leaf nodes and root nodes except the root node itself. The technology can be further extended to a generic solution with a root VLAN and a leaf VLAN, that is, all leaf nodes reach the root nodes by a leaf VLAN, and all root nodes reach all leaf nodes and other root nodes by a root VLAN.
Virtual private local area network service (Virtual Private LAN Service, VPLS) is a technology for emulating the Ethernet LAN by using the wide area network (Wide Area Network, WAN) architecture. The VPLS is capable of providing multipoint-to-multipoint connection in a Multi Protocol Label Switching (Multi-Protocol Label Switch, MPLS) network. This facilitates users' access to the MPLS network from multiple geographically dispersed points, and helps users' access to each other, which is similar to accessing a LAN directly from these points. At present, core network commonly uses the Internet Protocol (Internet Protocol, IP)/MPLS technology. Therefore, the requirements on providing virtual Ethernet services by using the VPLS is increasing and the deployment has seen wide application.
In a traditional implementation of the architecture of a provider edge (Provider Edge, PE) device and E-Tree service in VPLS, multiple CE nodes access a customer virtual local area network (Customer Virtual Local Area Network, C-VLAN) bridge (performing C-VLAN encapsulation) by using an attachment circuit (Attachment Circuit, AC), the C-VLAN bridge attaches to a service virtual local area network (Service VLAN, S-VLAN) bridge (performing S-VLAN encapsulation), the S-VLAN bridge connects to a virtual switch instance (Virtual Switch Instance, VSI) of the VPLS by using a virtual Ethernet interface, and then connects to the VSIs of other PE devices each by an end-to-end PW. For example, Ethernet frames of a customer are imported from the AC to the C-VLAN bridge. The C-VLAN bridge tags the Ethernet frames with a C-VLAN identifier, and sends the Ethernet frames to the S-VLAN bridge by using a virtual interface. At the ingress of the S-VLAN bridge, the frames are further tagged with a S-VLAN identifier. If the frames belong to a specific VPLS instance, they arrive at the VSI through the virtual interface of an S-VLAN corresponding to the VPLS instance. In current MPLS/VPLS network, valid isolation between the E-Tree leaf nodes cannot be guaranteed.
In MPLS/VPLS network, the critical issues presented in the industry lie in how to realize a valid isolation between E-Tree leaf nodes and ensure the original scalability of the VPLS.